The treatment of chronic and non-chronic pain conditions has great importance in medicine. There is a worldwide need for effective methods of treating pain. The urgent need for action for patient-friendly and purposeful treatment of chronic and non-chronic pain conditions, this being taken to mean the successful and satisfactory treatment of pain for the patient, is documented in the large number of scientific papers which have recently appeared in the field of applied analgesics and fundamental research work on nociception.
Conventional opioids, such as morphine, are extremely effective in the treatment of severe to the severest pain. However, their use is limited by the known side effects, for example respiratory depression, nausea, sedation, constipation and tolerance development. In addition, they are less effective in the event of neuropathic or incidental pain, from which patients with tumors suffer in particular.
Opioids deploy their analgesic effect by binding to membrane receptors belonging to the family known as G-protein-coupled receptors. The biochemical and pharmacological characterization of subtypes of these receptors has now roused hopes that subtype-specific opioids have a different profile of effects and side effects from, for example, morphine. Further pharmacological investigations have in the meantime affirmed the likelihood of the existence of a plurality of subtypes of these opioid receptors (μ1, μ2, κ1, κ2, κ3, δ1 and δ2).
There are further receptors and ion channels which participate substantially in the pain development and pain transmission system, for example the so-called batrachotoxin-(BTX) binding site (=binding site 2) of the sodium channel or the NMDA ion channel through which a substantial proportion of synaptic communication takes place by controlling the exchange of calcium ions between the neuronal cell and its environment.